The invention relates to an apparatus and method for impregnating fiber material with treatment liquid, especially with digesting liquid, before treatment of the fiber material, especially before digestion thereof. The pre-impregnation of fiber material with treatment liquid constitutes a very important part of the delignifying process in the production of pulp, the object of the pre-impregnation being to replace the air or gas content of the fiber material with the impregnation liquid. Conventionally, the air or gas is replaced by the utilization of steam at a small super-atmospheric pressure, followed with the submersion of the fiber material in treatment liquid at higher pressure and temperature. Also, initial vacuum treatment and pressing, followed by submersion in treatment liquid, is known. Whatever prior art conventional methods are utilized, a certain amount of equipment is necessary. it is desirable -- both for economical and space saving reasons -- to limit the amount of impregnation equipment necessary as much as possible. At the same time, no decrease in the efficiency of the impregnation process is tolerable.
Swedish Pat. No. 174,656 teaches the impregnation of fiber material by pressure variations of the impregnating liquid. According to the teachings of this Swedish patent, the readily-impregnable fiber material is led away from an impregnation chamber more quickly than the less readily-impregnable fiber material. The impregnation vessel is a long, sloping structure to which a mixture of fiber material and digesting liquor at pressure is fed by means of one assembly, and is withdrawn by means of another assembly. A conveyor for the impregnated fiber material is disposed within the impregnation vessel, and the air that is displaced is withdrawn, and the pressure variations are obtained by means of a vacuum pump and/or a liquor tap-off means. The structure of the Swedish patent is relatively complex, a great deal of accessory equipment being necessary.
According to the apparatus and method of the present invention, impregnation through pressure variations may take place with the utilization of a minimum amount of accessory equipment. Essentially, according to the present invention, the only accessory equipment that is necessary is a valve in a conduit in the treatment vessel (and various pressure sensitive and time and pressure responsive control means for the valve) and a screening device. A conventional continuous digester or other treatment vessel and conventional pocketed-rotor transfer device, such as devices produced by Kamyr Inc., may be utilized, along with a feed system such as shown in U.S. Pat. No. 3,802,956. The apparatus, according to the present invention, includes a relatively low pressure first system including a source of fiber material in treatment liquid, a means for continuously removing liquid from the first system to maintain the system at relatively low pressure, means for transferring fiber material in treatment liquid in the first system to a second relatively high pressure system (said means including a conventional Kamyr high pressure pocketed-rotor transfer device), a conventional Kamyr high pressure vertical fiber material treatment vessel (i.e., digester), the second pressure system including an upper impregnation portion of the fiber material treatment vessel, means for selectively allowing or blocking communication between the second system and the fiber material treatment vessel so that the pressure in the second system is substantially as high as the treatment vessel pressure when communication between the second system and the the treatment vessel is allowed, and so that the pressure in the second system becomes significantly reduced when communication between the second system and the treatment vessel is terminated, and timing means for controlling the selective communication means to control the relative times the second system is exposed to high and low pressure so that impregnation of fiber material with treatment liquid takes place in the second system. The fiber material and liquid in the first system may be at a small super-atmospheric pressure of about 1 atmosphere, while the digester pressure (and the pressure phase in the second system during the high pressure thereof) is about 10 atmospheres. The conventional transmission device utilized for providing transfer of fiber material and liquid from the first system to the second system operates so that the flow between the first system and the second system is substantially continuous. (Steam treatment of the fiber material before it is actually fed to the transmission device is possible to remove the majority of the air in the fiber material.) Complete impregnation of the fiber material with treatment liquid takes place in the second system.
According to the method of impregnating fiber material with treatment liquid, according to the present invention (utilizing a high pressure treatment vessel having an upper impregnation chamber), a first flow system of fiber material and treatment liquid under relatively low pressure is established, liquid is continuously withdrawn from the first system so the pressure therein is reduced unless supplemental liquid is provided, a second flow system of fiber material and treatment liquid under relatively high pressure is established, fiber material in treatment liquid in the first system is transferred to the second system, the second system including the impregnation chamber of the fiber material treatment vessel, communication between the second system and the treatment vessel is selectively allowed or blocked so that the pressure in the second system is substantially as high as the treatment vessel when communication between the second system and the second treatment vessel is allowed, and so that the pressure in the second system becomes significantly reduced when communication between the second system and the treatment vessel is blocked, and the time that communication between the second system and the treatment vessel is effected is controlled so that the relative times that the second system is exposed to high and low pressure is controlled so that impregnation of fiber material with treatment liquid takes place in the second system.
It is the primary object of the present invention to provide an improved method and apparatus for the impregnation of fiber material with treatment liquid, by effecting the impregnation through pressure fluctuation in a simple system. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and the appended claims.